Lens polishing composition containing diamonds in an epoxide resin matrix

ABSTRACT

The use of tiny diamonds for finish polishing of glass lenses has been made possible by incorporating them into a lap material comprising very small diamonds in a special polymeric matrix of the reaction product of an organic epoxide with an appropriate &#39;&#39;&#39;&#39;hardener,&#39;&#39;&#39;&#39; such as a polyamine.

United States Patent 1 Valerio et al,

[ Jan. 30, 1973 [541 LENS POLISHING COMPOSITION CONTAINING DIAMONDS INAN EPOXIDE RESIN MATRIX [75] Inventors: Paul F. Valerio; Robert M.Werner,

both of Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[22] Filed: Jan. 2, 1969 [21] Appl. No.: 788,655

[51] Int.C1. ..C08g 51/12 [58] Field of Search ..51/293, 295, 298

[56] References Cited UNITED STATES PATENTS 2,860,961 11/1958 Gregor eta1. ..5l/298 2,939,777 6/1960 Gregor et al. 51/298 2,944,879 7/1960Allen et all ..5l/308 3,226,214 12/1965 Daniels el al.. "51/298.3,102,011 8/1963 Bellinger ..5 H298 Primary Examiner-Donald .1. ArnoldAttorney-Walter O. Hodsdon, Paul R. Holmes and John T. Lewis [57]ABSTRACT 10 Claims, No Drawings LENS POLISHING COMPOSITION CONTAININGDIAMONDS IN AN EPOXIDE RESIN MATRIX This invention relates to opticalpolishing materials and methods for use and manufacture thereof.

Lenses and other optical elements are commonly manufactured by grindingsuch elements to the approximate shape desired and then polishing toremove scratches created in grinding. A small amount of shaping can alsobe done'in polishing. One type of grinding process is carried out in oneor more steps using a material made of finely crushed and carefullygraded diamonds embedded in sinteredor friable metal. The grindingeffect can be made either coarse or fine not only by the size of thediamonds used, but also by the character of the sintered metal bondingthe diamonds. For example, if the bond is made quite close, the friablepart of the metal does not break away as readily and tends to give afiner grind than does a more open sinter. In the grinding operation, acoolant is necessary.

After one or more grinding steps have been performed on a lens, thescratches created in grinding give the surface of the lens a frostedappearance. This frosted appearance is removed by polishing. A commonmethod of polishing involves use of a nonabrasive wax lap combined witha coolant containing an abrasive such as rouge or ceric oxide. It isbelieved that friction created with the polishing composition andrubbing pressure from the wax heats the surface, thereby giving it atendency to flow. The material from the ridges of a scratch flow intothe depressions of the scratch, thereby eliminating the scratch andmaking the surface optically usable. It is also believed that someabrasion of the ridge occurs simultaneously.

In the course of the polishing operation, the wax itself has a tendencyto flow, thereby filling up indentations which have been cut in the waxfor application of polishing composition and coolant. As theseindentations are filled up, the operator must recut them or there willbe no room for the coolant. Similarly, as the wax flows, it tends tochange its shape which in turn has a tendency to change the shape of thelens surface being polished resulting in an inaccurate test-glass fit.Additional polishing steps with a more accurate lap are often used toobtain a good test-glass fit.

In any polishing operation, the polishing compound in the coolantcreates a substantial cleaning problem.

Occasionally, with certain materials, a slurry charged with diamondparticles of submicron size has been used as the abrasive-coolant in thepolishing operation. In general, this has not been successful for highquality glass lens production.

It is an object of this invention to provide an optical polishing lapmaterial having greatly increased life.

It is another object of this invention to sharply reduce or eliminatethe need for polishing compositions in the coolant in an optical glasspolishing operation.

It is another object of this invention to provide a lens polishingmethod which requires reduced operator attention.

It is another object of this invention to provide a lap material foroptical polishing in which the tendency to flow is reduced or sharplyeliminated.

It is another object of this invention to provide a lens polisher whichhas a tendency to give a superior testglass fit.

-It is another object of this invention to provide polished glass lenseshaving improved sub-surfaces or substrates (just under the surfaces).

These and other objects are accomplished by manufacture and use of a newlap material for lens polishing. This lap material contains crusheddiamonds in a plastic bond thereby supplying the polishing abrasive inthe lap material rather than in the coolant. The finely crusheddiamonds, surprisingly, operate as polishing abrasives. When bonded in aproper matrix according to the invention the use of diamonds does notresult in a scratched optical surface, but instead, results in a highlypolished surface.

It is thus a feature and object of this invention to provide a matrix orbond containing tiny diamonds. With this diamond-matrix lap material,glass can be finish polished" without being scratched. Such a bondconstructed according to the invention includes an epoxide which hasbeen polymerized with an appropriate epoxide hardener while the diamondparticles are distributed therein. Through out a long life, this bond ormatrix somehow holds the diamond particles in such a manner as toprevent grinding or scratching, and to aid the diamonds in polishing theglass.

With the use of this lap material, the following remarkable results canbe obtained:

Diamonds which can be crushed and graded to the same size as grinding"diamonds do not scratch or grind the glass, but polish it;

The polisher (lap material) can be made to provide an order of magnitudemore wear than conventional polishers; and

The polishing compound in the coolant can be eliminated or sharplyreduced, thereby reducing operator attention in cleaning.

The valuable lap materials of this invention can be manufactured by (a)blending together (1) an appropriate organic epoxide compound having anepoxide equivalent of from about 150 to about 450, wherein the epoxidecontains an average of at least about 1.5 (preferably about 2) epoxideunits or groups per molecule, (2) an appropriate hardener, and (3) fromabout 5 to about weight percent of diamonds having diameters of fromabout 1 to about 50 microns, and (b) thereafter permitting a reactionbetween the epoxide and the hardener" to occur (preferably by warmingthe blend in an oven at elevated temperatures up to 250 F or more) tothereby produce the valuable lap materials of this invention. It canreadily be appreciated that these lap materials can be shaped in anydesired manner by permitting the epoxidation reaction to occur while thematerials are contained in a mold, for example. In this manner pelletsor shaped polishing blocks of practically any desired size andconfiguration can be obtained.

Preferred organic epoxide materials are those having and havingthe basicbisphenol structure:

wherein R contains from zero to eight carbon atoms, and X can resultfrom reaction with another bisphenol or bisphenol epoxide. Suchbisphenol epoxides and modified bisphenol epoxides are well known in theart .and need not be described in great detail herein.

Preferred hardeners (for reaction with the epoxide compounds thatareuseful in the practice of this invention to thereby convert the liquid(or thick fluid) epox-' ide into the desired, solid matrix) are thoseorganic amines having molecular weights of at most about 200. Typical,non-limiting examples of such preferred hardeners include, piperidine,pyridine, diethylene triamine, dimethyl-aminopropylamine,benzyldimethylamine, diethylenediamine, diethylaminopropylamine,dibutylaminopropylamine, metaphenylenediamine, triethylene tetramine,and dicyandiamide. Usage of such amine hardeners is generally in amountscalculated so that from about 0.5 to about 1.5 (and preferably about1.0) active amine groups are present in the blend per epoxide unit orgroup.

In the practice of this invention, it has been found that atleast about50 weight percent of the final lap material must be represented byproduct(s) of the epoxide-hardener reaction. Materials other thandiamonds and epoxide-hardener matrix material can also be present in thelap materials of this invention (in minor amounts up to about 20 weightpercent). For example, it is believed that the inclusion of up to aboutweight percent of a phenyl glycidyl ether (a monofunctional epoxide),when included into the original blend of materials, functions as abeneficial plasticizer and/or extender in the final, hardened lapmaterial of this invention. Similarly, dyes and pigments and polyvinylacetate can be present in the lamp materials of this invention, ifdesired, without detracting substantially from the valuable benefitsthat can be obtained by 7 practicing it.

Also, it has been discovered that the presence, in the lap materials ofthis invention, of up to as much as about 50 volume percent of fairlyuniformly dispersed gas bubbles (which appear as holes in the final,hardened lap material) actually significantly improves the efficiency ofthe hardened lap material. Such bubbles can be forced into the lapmaterial by simply beating (or stirring intensively) the fluid blend ofepoxide plus hardener plus diamonds to thereby disperse air through theblend, and thereafter hardening the matrix while the air bubbles remainentrapped in the matrix. There should generally be at least about 5volume percent of such gas bubbles (as compared with the unaeratedvolume of the blend), whereas the preferred volume of gas is from about15 to about 35 percent. I

The final solidified lap materials of this invention should preferablycontain from about 10 to about 25 weight percent of diamonds havingdiameters of from about I to about 50 microns, and substantially nodiamonds having diameters as great as 60 microns. The diamonds in thepreferred compositions of this inven tion have average diameters of fromabout 5 to about 20 microns, while still further preferred are thosediamonds having diameters ranging from about 8 to about 16 microns, withtheir number average diameter being about 12 microns.

One of the most surprising aspects of this invention relates to the factthat the use of diamonds in accordance herewith results in polishing,rather than grinding. Heretofore, it is believed that there was no wayknown to accomplish this. Diamonds were believed to scratch too much tobe useful in the finish polishing operations of glass lens manufacture.Apparently it is the peculiar combination of ingredients (small diamondsin the epoxy-hardener matrix) that makes this valuable effect possible,because it is apparently-only inthis way that acceptable polishing withdiamonds can be accomplished.

Still another surprising aspect of the present invention relates to thefact that glass finish polishing can be accomplished using the lapmaterials of this invention in the essential absence of other polishingcompositions. This is particularly advantageous in most instances inthat it makes possible the elimination of not only expensive recovery(for reuse) of polishing compositions, as well as elimination of thefairly expensive polishing composition itself, but also, it cansignificantly simplify the final cleaning step, as compared with that ofprocesses that involve the use of conventional polishing compositions.

One of the most valuable contributions of the present invention to theart of glass polishing can readily be appreciated from the fact that thelap materials of this invention have useful lives of as much as 10 ormore times that of most conventional lap materials used in high speedpolishing. Still another surprising aspect of this development can beappreciated from the fact that lenses polished with the lap materials ofthis invention have substantially fewer sub-surface scars, andsubstantially better overall performance characteristics than havelenses polished via practically any conventional method.

In the following examples, all parts" given are by weight unlessotherwise stated.

EXAMPLE 1 Into a conventional stainless steel mixer are poured 763 partsof a modified bisphenol A epoxide having an epoxide equivalent of 200(sold by Ciba Corporation under the trade name Araldite 502 Epoxy), 57parts of diethylene triamine hardener, and 164 parts of diamond powder(U.S. B. S. No. 12), with particles having an .average diameter of about12 microns and a range of diameter from 8 to 16 microns. The mixture isstirred vigorously to whip about 20 volume percent of air into it. Thenit is poured into molds to form round pellets or discs one-eighth inchhigh and one-half inch in diameter. The molds are cured at 210 F for 12hours. The resulting solid pellets or laps" are mounted on aconventional curved block (wherein the radius of curvature around thetop surfaces of the pellets equals the desired radius of curvature ofthe final polished glass elements). Lenses to be polished are mounted ona block (with their top surfaces exposed) having the opposite shape.During the polishing operation, the block holding the lenses is rotatedat high speed about the vertical axis. In addition the block holding thelap is oscillated backward and forward and allowed to turn freely on aspinner being separated from the other block only by a coolant or apolishing slurry. Starting with ground lenses, only a few minutes arerequired to finish polish the lenses using the laps prepared in theforegoing manner. The surfaces of the resulting lenses are found to bebrilliant, to have excellent optical quality, and to have a lower levelof subsurface defects than are usually obtained in lenses ground usingconventional polishing compositions such as ceric oxide or ferioxiderouge, for example.

EXAMPLE 2 Laps are prepared as in Example 1, except that 16 parts ofsilica aerogel (thickening material sold by Cabot Labs under the tradename Cab-O-Sil) are blended into the material to aid in the entrapmentof air thereinto. Also, curing of the laps is accomplished this time at160 F for 12 hours. Excellent lens polishing results, similar to thoseof Example 1, are obtained using the resulting laps.

EXAMPLE 3 Example 1 is repeated, except that the diamond powder isreplaced with Cerox (a conventional cerium oxide polishing compound).Lenses polished with the resulting solid laps are scratched excessivelyand not really polished acceptably.

EXAMPLE 4 Example 1 is repeated, except that the diamond powder isreplaced with SOO-mesh ground glass. Lenses polished with the resultingsolid laps are scratched excessively, and not polished acceptably.

EXAMPLE 5 Example 1 is repeated, except that half of the diamond powderis replaced with SOD-mesh ground glass. Unsatisfactory results similarto those from Example 4 are obtained.

EXAMPLE 6 Example 1 is repeated, except that Shell 828 Epoxy is used asthe epoxide material and- 80 parts of triethylene tetramine hardener isused (in place of the diethylene triamine). In addition, 24 parts of thesilica aerogel thickener is mixed into the blend. The resulting blend iscured first for 12 hours at room temperature and then for 5 hours at 160F. The resulting laps show wear rates five times as long as those ofconventional wax laps. The use of these laps in lens polish ingoperations results in excellent polished surfaces on the lenses.

EXAMPLE 7 Example 6 is repeated using 80 parts additional ofmonoepoxidized alkyl glycidyl ether in the initial blend. The resultingsolid lap material finish polishes glass lenses in a manner fullycomparable to that of the laps of Example 6.

EXAMPLE 8 Example 1 is repeated, except that 9 micron diameter emery(aluminum oxide) is substituted for the diamond powder. Unacceptablyscratched lenses result from attempts to use the resulting laps tofinish polish glass lenses.

EXAMPLE 9 Example 1 is repeated without the diamond powder. Theresulting laps wear out quickly, and polish glass lenses very slowly.

EXAMPLE 10 Example 1 is repeated, except that the epoxide and hardenerare replaced with sintered nylon powder (sold by the Polymer Corporationunder the trade name Nylasint No. 66). The blend is pressed in a moldunder pressure of 3.5 tons, and then sintered for 1 hour at 45 0F. Wearrates for the resulting laps are found to be excessively high.

Other epoxide materials having the above-described requisite activity,as well as other well known hardeners for such epoxides can besubstituted accordingly into Example 1, above to yield useful lapmaterials for lens polishing, in accordance with this invention.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:

l. A lap material suitable for finish polishing the surface of glasslenses having improved properties; said lap material containing fromabout 5 to about 50 weight percent of diamonds having diameters of fromabout 1 to about 50 microns dispersed through and supported by a solidmatrix; said solid matrix consisting essentially of the epoxide resinproduct of the reaction of (a) an organic epoxide compound having anepoxide equivalent of from about to about 450 with (b) an organic aminehardener; said amine having a molecular weight of at most about 200, andsubstantially all of said diamonds having diameters below 60 microns,and said epoxide resin product being present in said lap material in anamount equal to at least about 50 weight percent of said lap material.

-2. A lap material as in claim 1, wherein said lap material alsocontains gas bubbles dispersed through said matrix; the total volume ofsaid gas being from about 5 to about 50 percent of the unaerated volumeof said lap material.

3. A lap material as in claim 2, wherein said organic epoxide compoundhas an epoxide equivalent of from about to about 300, and said organicamine is an organic polyamine.

4. A lap material as in claim 3, wherein said organic polyamine is apolyalkyl polyamine.

5. A lap material as in claim 4, wherein said organic epoxide materialis a modified bisphenol epoxide, containing an average of at least about1.5 epoxide units per molecule.

6. A lap material as in claim 5, wherein the average particle sizeofsaid diamonds is about 12 microns; said lap material being substantiallyfree of diamonds having diameters greater than 60 microns; the amount ofsaid diamonds in said lap material being from about 10 to about 25weight percent and the amount of said gas in said lap material beingfrom about 15 to about 35 volume percent.

epoxide material contains an average of at least about 1.5 epoxide unitsper molecule and has an epoxide equivalent of from about to about 450,and the amount of said organic polyamine is equal to from about 0.5 toabout 1.5 amine groups per epoxide group.

10. A lap material as in claim 9, wherein said polyamine is'a polyalkylpolyamine.

1. A lap material suitable for finish polishing the surface of glasslenses having improved properties; said lap material containing fromabout 5 to about 50 weight percent of diamonds having diameters of fromabout 1 to about 50 microns dispersed through and supported by a solidmatrix; said solid matrix consisting essentially of the epoxide resinproduct of the reaction of (a) an organic epoxide compound having anepoxide equivalent of from about 150 to about 450 with (b) an organicamine hardener; said amine having a molecular weight of at most about200, and substantially all of said diamonds having diameters below 60microns, and said epoxide resin product being present in said lapmaterial in an amount equal to at least about 50 weight percent of saidlap material.
 2. A lap material as in claim 1, wherein said lap materialalso contains gas bubbles dispersed through said matrix; the totalvolume of said gas being from about 5 to about 50 percent of theunaerated volume of said lap material.
 3. A lap material as in claim 2,wherein said organic epoxide compound has an epoxide equivalent of fromabout 175 to about 300, and said organic amine is an organic polyamine.4. A lap material as in claim 3, wherein said organic polyamine is apolyalkyl polyamine.
 5. A lap material as in claim 4, wherein saidorganic epoxide material is a modified bisphenol epoxide, containing anaverage of at least about 1.5 epoxide units per molecule.
 6. A lapmaterial as in claim 5, wherein the average particle size of saiddiamonds is about 12 microns; said lap material being substantially freeof diamonds having diameters greater than 60 microns; the amount of saiddiamonds in said lap material being from about 10 to about 25 weightpercent and the amount of said Gas in said lap material being from about15 to about 35 volume percent.
 7. A lap material as in claim 2, whereinsaid lap material also contains from about 0.5 to about 5 weight percentof a silica thickening agent.
 8. A lap material as in claim 3, whereinsaid lap material contains from about 10 to about 25 weight percent ofdiamonds having diameters of from about 8 to about 16 microns.
 9. A lapmaterial as in claim 8, wherein said organic epoxide material containsan average of at least about 1.5 epoxide units per molecule and has anepoxide equivalent of from about 150 to about 450, and the amount ofsaid organic polyamine is equal to from about 0.5 to about 1.5 aminegroups per epoxide group.